They don't. The 4017 can only handle a few milliamps (mA). But by using a FET transistor, Q1 in the bike blinker project, between the 4017 and the Luxeon LED the current is "amplified" (not scientifically true, but close enough for this discussion). The FET can handle several amps without breaking a sweat. So by connecting a FET transistor between each of the ten outputs of the 4017 and the LED's the weak output of the 4017 is just turning on the transistor which in turn can handle the high load of the Luxeon.

FEATURED

Ask A Maker If you've found your way here via Ask A Maker … welcome to Instructables! The first 20 commenters will…

Mystery Prizes!What's more fun that winning a prize? Why winning a mystery prize, of course! We're sending out mystery pri…

Profile Page UpdatesHello Everyone!
Many of you have noticed and commented on the site updates that went live on Thursday, Oct…